As a semiconductor device, insulated gate-type transistors such as a Metal Oxide Semiconductor Field Effect Transistors (MOSFET) or an Insulated Gate Bipolar Transistors (IGBT) are used. In the semiconductor device, low-power consumption by virtue of a low on-state resistance is required. To realize the low on-state resistance of the MOSFET, a MOSFET having a field plate electrode with a source potential, formed via an insulating film in a trench extending deep into the drift layer, and a gate electrode sandwiched, via an insulating film, between a p-type base layer and the field plate electrode at the upper end of the field plate electrode, has been developed. In the MOSFET, a depletion layer extends into an n−-type drift layer from the adjacent field plate electrodes, thus being able to easily deplete the entire n−-type drift layer. For this reason, in the MOSFET, the on-state resistance can be lowered by raising the n-type impurity concentration of the n−-type drift layer. However, since the field plate electrode with a source potential and the gate electrode with a gate potential are overlapped via the insulating film, the gate-source capacitance is increased. As a result, even if the on-state resistance is lowered, the product (R•C product) of the on-state resistance and the input capacitance as an index of the performance of a semiconductor device is increased.